It is known to include in textile yarns metallic wires and to include metallic surface coatings on yarns for the purpose of carrying electrical current, performing an anti-static electricity function or to provide shielding from electric fields. Such electrically conductive composite yarns have been fabricated into fabrics, garments and apparel articles.
It is believed impractical to base a conductive textile yarn solely on metallic filaments or on a combination yarn where the metallic filaments are required to be a stressed member of the yarn. This is due to the fragility and especially poor elasticity of the fine metal wires heretofore used in electrically conducting textile yarns.
Sources of fine metal wire fibers for use in textiles include, but are not limited to: NV Bekaert SA, Kortrijk, Belgium; Elektro-Feindraht AG, Escholzmatt, Switzerland and New England Wire Technologies Corporation, Lisbon, N.H. As illustrated in FIG. 1a such wires 10 have an outer coating 20 of an insulating polymeric material surrounding a conductor 30 having a diameter on the order of 0.02 mm-0.35 mm and an electrical resistivity in the range of 1 to 2 microohm-cm. In general, these metal fibers exhibit a low force to break and relativity little elongation. As shown in FIG. 2 these metal filaments have a breaking strength in the range of 260 to 320 N/mm2 and an elongation at break of about 10 to 20%. However, these wires exhibit substantially no elastic recovery. In contrast, many elastic synthetic polymer based textile yarns stretch to at least 125% of their unstressed specimen length and recover more than 50% of this elongation upon relaxation of the stress.
U.S. Pat. No. 3,288,175 (Valko) discloses an electrically conductive elastic composite yarn containing nonmetallic and metallic fibers. The nonmetallic fibers used in this composite conducting yarn are textile fibers such as nylon, polyester, cotton, wool, acrylic and polyolefins. These textile fibers have no inherent elasticity and impart no “stretch and recovery” power. Although the composite yarn of this reference is an electrically conductive yarn, textile material made therefrom fail to provide textile materials having a stretch potential.
Similarly, U.S. Pat. No. 5,288,544 (Mallen et al.) discloses an electrically conductive fabric comprising a minor amount of conductive fiber. This reference discloses conductive fibers including stainless steel, copper, platinum, gold, silver and carbon fibers comprising from 0.5% to 2% by weight. This patent discloses, by way of example, a woven fabric towel comprising polyester continuous filaments wrapped with carbon fibers and a spun polyester (staple fiber) and steel fiber yarn where the steel fiber is 1% by weight of the yarn. While fabrics made from such yarns may have satisfactory anti-static properties apparently satisfactory for towels, sheets, hospital gowns and the like; they do not appear to possess an inherent elastic stretch and recovery property.
United States Patent Application 2002/0189839A1, published 19 Dec. 2002, (Wagner et al.), discloses a cable to provide electrical current suitable for incorporation into apparel, clothing accessories, soft furnishings, upholstered items and the like. This application discloses electric current or signal carrying conductors in fabric-based articles based on standard flat textile structures of woven and knitted construction. An electrical cable disclosed in this application includes a “spun structure” comprising at least one electrically conductive element and at least one electrically insulating element. No embodiments appear to provide elastic stretch and recovery properties. For applications of the type contemplated the inability of the cable to stretch and recover from stretch is a severe limitation which limits the types of apparel applications to which this type of cable is suited.
Stretch and recovery is an especially desirable property of a yarn, fabric or garment which is also able to conduct electrical current, perform in antistatic electricity applications or provide electric field shielding. The stretch and recovery property, or “elasticity”, is ability of a yarn or fabric to elongate in the direction of a biasing force (in the direction of an applied elongating stress) and return substantially to its original length and shape, substantially without permanent deformation, when the applied elongating stress is relaxed. In the textile arts it is common to express the applied stress on a textile specimen (e.g. a yarn or filament) in terms of a force per unit of cross section area of the specimen or force per unit linear density of the unstretched specimen. The resulting strain (elongation) of the specimen is expressed in terms of a fraction or percentage of the original specimen length. A graphical representation of stress versus strain is the stress-strain curve, well-known in the textile arts.
The degree to which fiber, yarn or fabric returns to the original specimen length prior to being deformed by an applied stress is called “elastic recovery”. In stretch and recovery testing of textile materials it is also important to note the elastic limit of the test specimen. The elastic limit is the stress load above which the specimen shows permanent deformation. The available elongation range of an elastic filament is that range of extension throughout which there is no permanent deformation. The elastic limit of a yarn is reached when the original test specimen length is exceeded after the deformation inducing stress is removed. Typically, individual filaments and multifilament yarns elongate (strain) in the direction of the applied stress. This elongation is measured at a specified load or stress. In addition, it is useful to note the elongation at break of the filament or yarn specimen. This breaking elongation is that fraction of the original specimen length to which the specimen is strained by an applied stress which ruptures the last component of the specimen filament or multifilament yarn. Generally, the drafted length is given in terms of a draft ratio equal to the number of times a yarn is stretched from its relaxed unit length.
Elastic fabrics having conductive wiring affixed to the fabric for use in garments intended for monitoring of physiological functions in the body are disclosed in U.S. Pat. No. 6,341,504 (Istook). This patent discloses an elongated band of elastic material stretchable in the longitudinal direction and having at least one conductive wire incorporated into or onto the elastic fabric band. The conductive wiring in the elastic fabric band is formed in a prescribed curved configuration, e.g., a sinusoidal configuration. The elastic conductive band of this patent is able to stretch and alter the curvature of the conduction is wire. As a result the electrical inductance of the wire is changed. This property change is used to determine changes in physiological functions of the wearer of a garment including such a conductive elastic band. The elastic band is formed in part using an elastic material, preferably spandex. Filaments of the spandex material sold by DuPont Textiles and Interiors, Inc., Wilmington, Del., under the trademark LYCRA® are disclosed as being a desirable elastic material. Conventional textile means to form the conductive elastic band are disclosed, these include warp knitting, weft knitting, weaving, braiding, or non-woven construction. Other textile filaments in addition to metallic filaments and spandex filaments are included in the conductive elastic band, these other filaments including nylon and polyester.
While elastic conductive fabrics with stretch and recovery properties dominated by the spandex component of the composite fabric band are disclosed, these conductive fabric bands are intended to be discrete elements of a fabric construction or garment used for prescribed physiological function monitoring. Although such elastic conductive bands may have advanced the art in physiological function monitoring they have not shown to be satisfactory for use in a way other than as discrete elements of a garment or fabric construction.
In view of the foregoing it is believed desirable to provide a conductive textile yarn with elastic recovery properties which can be processed using traditional textile means to produce knitted, woven or nonwoven fabrics, Further, it is believed that there is yet a need for fabrics and garments which are substantially wholly constructed from such elastic conductive yarns. Fabrics and garments substantially wholly constructed from elastic conductive yarns provide stretch and recovery characteristic to the entire construction, conforming to any shape, any shaped body, or requirement for elasticity.